Excretion

Question 1

What is excretion

Answer 1

The metabolic processes that take place within the body produce a variety of waste products, such as CO2 ammonia, urea and uric acid.

The accumulation of these waste products within a cell would have a negative impact on its normal functioning.

Therefore , Excretion is the removal of waste products from the body. Several organs and processes contribute to the transport and elimination of these products.

Question 2

List the excretory organs

Answer 2

Lungs
Skin
Liver
Colon
Kidney

Question 3

For reach organ give the waste product, the origin and the excrete product

Answer 3

Lungs
carbon dioxide and water
vapour

cellular respiration

COz and H20(g) in exhaled air

———————————————
Skin (sweat glands) mineral salts, traces of urea, water

extracted from the blood

Question 4

Hays does the excretory system of humans consist of

Answer 4

two kidneys,
two ureters,
a bladder,
and the urethra
It’s associated blood supply : renal artery and renal vein

Question 5

What’s is the function of the excretory system

Answer 5

to remove the toxic, poisonous substance urea,
other waste salts
and excess of water from the blood
and excrete them in the form of a yellowish liquid called urine.

Question 6

Define
Ureters
Bladder
Urethra

Answer 6

Ureters: Ducts that carry urine from each kidney to the bladder.

Bladder: Located in the pelvic cavity, it serves to store urine prior to urination.

Urethra: A tube leading from the bladder to the exterior through which urine (and semen males) is

Question 7

What’s re the 4 mainfunctions if the urinary system

Answer 7

• Osmoregulation - regulation of levels of H20 in body fluids

• Excretion - removal of nitrogenous waste e.g. urea

• Regulation of pH of body fluids

• Regulation of salt concentration of body fluids

Question 8

Name the two internal sections of the kidney

Answer 8

The outer reddish part is called the renal cortex

The inner reddish-brownish part is called the renal medulla

Question 9

What tow parts make up the functional sort of the kidney

Answer 9

The renal cortex and the pyramids make up the functional portion of the kidney.

Question 10

What do y called the functional unit of the kidney

Answer 10

The nephron

Question 11

In similes words explain where urine is formed and how it drains into the bladder

Answer 11

Urine formed by the nephrons drains into papillary ducts, which lead into cup-shaped calyces.

The urine drains into the renal pelvis,

passes down the ureters,

enters the bladder

and eventually leaves the body via the urethra.

Question 12

Name the two components of the nephron

Answer 12

nephron - Malpighian body aka renal corpuscle( where plasma is filtered )and the renal tubule.( into which filtered fluid passes through)

Question 13

The renal corpuscle consists of two parts name these two parts

Answer 13

• the glomerulus: a dense capillary network in the hollowed part of the capsule

• the Bowman’s capsule(cup shape) : a double-walled cup that surrounds the glomerulus.

The outer wall of the sup has squamous epithelial cells.

The inner wall consists of modified cells called podocytes, which are in close proximity to the glomerular capillaries.

The podocyte cells have a finger like extension that wrap around the capillaries.

The podocytes and endothelial cells of the glomerular capillaries form a slit filtration membrane which acts as an ultra filter.

The space between the outer and inner walls of the Bowman’s capsule is called the capsular space.

Question 14

What does the renal tubule consist if

Answer 14

The renal tubule consists of three main parts:
1)the proximal convoluted tubule,

2) the loop of Henlé

3) the distal convoluted tubule.

Fluid from the capsular space passes into the renal tubules.

The distal convoluted tubules of a number of nephrons empty into a single collecting duct.

Collecting ducts unite to form papillary ducts which drain into calyces and then into the pelvis.

From the pelvis the urine passes into the ureter, which conveys it to the bladder.

The renal tubule is surrounded by a secondary capillary network known as the peritubular capillary network. Cuboidal epithelial cells line the renal tubule and have microvilli extensions on their surface. Each of these cells has a rich supply of mitochondria.
Energy supplied by cellular respiration can be used to move substances against a gradient.

Question 15

Explain the blood supple to the nephron

Answer 15

Therenal artery, a branch of the abdominal aorta, enters the kidney and branches into small arterioles. The afferent blood vessel divides into finer capillaries to form the glomerular capillaries, which reunite to form the efferent vessel. The efferent vessel divides to tom a etork of capilaries around the tubules. These blood vessels eventually unite to form the renal vein which then joins the inferior vena cava.

Question 16

Name the 3 stages of the functioning of the kidney

Answer 16

Glomerular filtration ( ultra filtration )

Tubular re absorption

Tubular excretion

Question 17

Explain glomerular filtration (ultra filtration

Answer 17

• Blood in the glomerulus is under pressure since the afferent vessel is larger in diameter than the efferent vessel.

• The increased pressure forces out both useful and harmful substances through the glomerulus and inner wall of the Bowman’s capsule, into the capsular

• The tiny pores in the capillary wall of the glomerulus and the specialised cells (called podocytes) forming the wall of the inner cup of the Bowman’s capsule, together form an ultra filter with slit pores, which selectively allow certain substances to pass through.

• Substances that pass through include: water, glucose, amino acids, urea and uric acid.

• Large substances like plasma proteins and blood cells do not filter through.

• The fluid, together with the dissolved substances, that enters the capsular space is called the glomerular filtrate.

• The glomerular filtrate contains both useful substances and waste products.

• The glomerular filtrate passes along the renal tubules.

Question 18

Explain tubular re absorption

Answer 18

• b) Tubular Reabsorption
The renal tubules consist of a single layer of cuboidal epithelial cells with brush border microvilli and numerous mitochondria. About 99% of the filtrate passing through the renal tubules is selectively reabsorbed; a process which is active (energy required), beginning at the capillary network of the proximal convoluted tubule.
• In the proximal convoluted tubule, some water and almost all the glucose and other useful substances are selectively reabsorbed by the second capillary network.
• The process of selective reabsorption is an active process requiring energy, which is obtained from the mitochondria of the cuboidal cells.
• The filtrate passes through the convoluted tubule and enters the loop of Henlé.
• The function of the loop of Henlé is to ensure that the medulla has a high concentration of sodium ions, i.e. a lo water potential when compared to the tubular fluid, to ensure that the maximum amount of water is removed from the tubular fluid.
• Sodium ions diffuse passively into the tubular fluid along the descending limb of the loop of Henlé.

Question 19

Explain the sodium pump

Answer 19

• Sodium ions diffuse passively into the tubular fluid along the descending loop of Henlé, whilst water leaves the tubular loop of Henlé, via osmosis.

• In order to facilitate the reabsorption of the
remaining water by osmosis, sodium ions are actively (energy involved) pumped out of the ascending limb of the loop of Henlé into the tissue
fluid of the medulla.

• This sodium pump mechanism ensures that the descending limb
water potential of the tubular fluid is raised.

• The concentration of solutes in the medulla is now
high, causing its water potential to be low.

• Water does not leave the ascending limb as its thicker walls are impermeable to water.

• In the distal convoluted tubule and collecting ducts, water is reabsorbed by osmosis out of the tubules and int the medulla, and finally back into the blood. Water is therefore conserved.

• The remaining fluid in the collecting tubule is known as urine.

• The antidiuretic hormone (ADH) regulates the re-absorption of water from the tubules into the blood capillarie

Question 20

Explain tubular excretion

Answer 20

c) Tubular excretion
The epithelial cells of the tubules also excrete substances into the tubules. Tubular excretion is the movement of substances from the blood into the tubular fluid. Excreted substances include hydrogen ions, potassium ions, ammonium ions, creatinine and certain drugs e.g. penicillin. The excretion of these substances into the tubules is an active (energy requiring) transport mechanism.
The pH of the blood is regulated by the amount of hydrogen ions (acid) and bicarbonate ions (alkaline) present. If the blood becomes too acidic, then the tubules extract more hydrogen ions from the blood; if too alkaline, then more bicarbonate ions are extracted.
Note: Ammonia is manufactured by the epithelial cells of the tubules (kidney metabolism) and excreted into tubular
The tubular fluid (urine) passes along the collecting tubule. A number of collecting tubules from other nephrons unite to eventually form a much larger tube called the duct of Bellini, which pours urine into the pelvis. The urine travels down the ureter, to the bladder when it is temporarily stored, until it is released to the exterior via the urethra.

Question 21

What are the The structural suitability of the kidneys in carrying out its functions

Answer 21

• The afferent blood vessel is wider than the efferent blood vessel. This causes a pressure build up in the glomerulus, which facilitates the filtration process.

• Podocytes of the Bowman’s capsule and endothelial cells of the capillaries form an effective filtration membrane.

• The cup-shape of the Bowman’s capsule allows for a close fitting of the glomerulus and a greater area for filtration.

• Cells of the tubules have brush border microvilli which provide a large surface area for selective reabsorption.

• The renal tubule is long and convoluted, allowing sufficient time for tubular reabsorption and excretion.

• A large number of mitochondria are present in the cells of the proximal convoluted tubule. This provides sufficient energy for active reabsorption to occur.